Sound pick-up device



March 1936. L. J. ANDERSON SOUND PICK-UP DEVICE Filed Feb. 18, 1935INVENTOR ATTORNEY Patented Mar. 3, 1936 UNITED STATES PATENT OFFICESOUND PICK-UP DEVICE Delaware Application February 18, 1935, Serial No.7,008

3 Claims.

This invention relates to sound pick-up devices such as that disclosedin United States Reissue Patent 19,115 of Harry F. Olson and JuliusWeinberger, and has for its principal object the provision of animproved arrangement of the acoustic labyrinth of the pressureresponsive element of such. devices.

As pointed out in the aforesaid patent, a sound pick-up device ormicrophone of the ribbon type may be operated in response both to thepressure of a sound wave and the pressuregradient of a sound wave byterminating a part of the ribbon diaphragm in a pipe or tube containingdamping material. Such a microphone has the advantage that its responseis substantially uniform throughout a comparatively wide angle. Theterminating tube or labyrinth as heretofore constructed, has resulted inincreasing the bulk of the microphone and milita'ting somewhat againstits appearance and portability. In accordance with this invention, thisdisadvantage is avoided by incorporating the labyrinth or acousticresistance tube in microphone. The invention will be better understoodfrom the following description when considered in connection with theaccompanying draw and its scope will be pointed out in the appendedclaims.

Referring to the drawing:

Fig. 1 is a perspective view of the improved microphone, and

Fig. 2 is a sectional view. of the acoustic labyrinth arranged tocooperate with the pressure gradient responsive section of themicrophone ribbon.

The microphone in Fig. 1 includes a corrugated ribbon diaphragm orconductor which is loosely suspended in an intense magnetic fieldproduced between the pole pieces H and I2 of a magnet I3 mounted on acasing 14 which may contain suitable amplifying equipment having itsinput circuit connected through leads 15 to the opposite ends of theloosely suspended ribbon l0. Mounted at the back of the ribbon I0 is atubular member IS, the mouth of which covers the lower section of thisribbon and communicates through tube 11 with the acoustic labyrinthcontained within the casing l8. Through lead IS the microphone amplifieris connected to suitable amplifying or other associated apparatus.

Fig. 2 shows the arrangement of the casing I8 and its relation to amicrophone stand provided with a base 2|. It will be observed that thecasing I8 is readily adjusted within the stand 20 by means of a thumbscrew 22 and a collar 23 and that a tube 24 communicating with the tubell extends into the adjustable casing I 8.

As explained in the aforementioned patent, the exposed or upper sectionof the ribbon l0 operates in response to the pressure gradient of thesound waves applied to it and the lower section of the ribbon, which isadjacent the opening of the tubular member 16, operates in response tothe pressure, of the sound wave. The phase relation of the voltagesgenerated in these sections is such that the directional responsecharacteristic of the microphone is approximately a cardiac ofrevolution.

The pressure operated portion of the microphone should theoretically beterminated in a tube of infinite length but is in practice terminated ina relatively long tube packed with damping material such as Ozite. Thepath of the damping cavity extends from the lower section of the ribbonI0 downwardly through tubes I1 and 24 and upwardly through tube I8 inthe annular space surrounding the tube 24. In a satisfactory microphoneconstruction in accordance with this invention, the length of this pathis 90 inches.

This arrangement of the acoustic resistance or damping path has theadvantage that it is better balanced mechanically, has a neaterappearance, is more readily moved from one position to another andpresents no difiiculty in the adjustment of the microphone height. Incases where additional damping space is desired the path may obviouslybe extended to include the microphone base.

Having thus described my invention, I claim:

1. The combination of a microphone mounted upon a support and providedwith a diaphragm one section of which is responsive to the pressuregradient of a sound wave, and means extending into said support forrendering another section of said diaphragm responsive to the pressureof said wave.

2. The combination of a microphone mounted upon a support and providedwith a diaphragm one section of which is responsive to the pressuregradient of a sound wave, means extending into said support forrendering another section of said diaphragm responsive to the pressureof said wave, and means for adjusting the height of said microphone.

3. The combination of a pick-up device ineluding a hollow support and adiaphragm, an

acoustic labyrinth extending into said support for rendering a part ofsaid diaphragm responsive to the pressure of a sound wave and forsupporting said diaphragm, and means for adjusting the position of saidlabyrinth within said support.

LESLIE J. ANDERSON.

